National Geographic News - 6.5.10

In the world’s driest places, “fossil water” is becoming as valuable as fossil fuel, experts say.

This ancient freshwater was created eons ago and trapped underground in huge reservoirs, or aquifers. And like oil, no one knows how much there is—but experts do know that when it’s gone, it’s gone.
“You can apply the economics of mining because you are depleting a finite resource,” said Mike Edmunds, a hydrogeologist at Oxford University in the Great Britain.

Bringing fossil water to the surface may cause other water quality issues. When aquifers are depleted, they can be subject to an influx of surrounding contaminants such as saltwater—a particular problem near coastal areas.

Also, like oil fields, depleting fossil water aquifers too quickly can reduce underground pressures and render large quantities of water essentially irretrievable.

Oxford’s Mike Edmunds said desert nations are only the obvious users of fossil water. In fact, many people may be using it, and using it up, without knowing.
“People think about quantity when they are pumping, they don’t ask about renewability as much—and that’s the big issue.”

Though determining the vintage of such water isn’t easy, said Duke’s Vengosh, telltale signatures can help: Scientists look for radioactive isotopes that have been present in Earth’s atmosphere only since humans initiated the nuclear era.

“In a very arid region one could argue that it doesn’t matter” how old the water is, Vengosh said. “But in semi-arid areas, the ability to delineate between fossil water and replenished groundwater is always important.”